1. Technical Field
The invention relates to voltage-controlled oscillator calibration and more particularly to integrated, automatic, on-chip voltage-controlled oscillator calibration.
2. Background of the Invention
A voltage-controlled oscillator (VCO) is an essential circuit in a phase-locked loop (PLL) system and is used to provide an output signal whose frequency is tunable with a control voltage (tuning voltage) typically referred to as Vtune. The tuning voltage typically varies from a minimum of about a fixed voltage V1 (e.g., 0.3 V) to a maximum voltage, typically referred to as VCC, minus a fixed voltage V2 (e.g. 2.7 V−0.5 V=2.2 V). Fixed voltages V1 and V2 are dependent on the type of charge pump that the PLL uses.
A VCO has a limited amount of tuning range. The tuning range depends, e.g., on the amount of tuning voltage Vtune that is available, and on a varactor used by the VCO. The ratio of the frequency range and the tuning voltage is referred to as VCO sensitivity (Kv). Low-sensitivity VCOs are often desirable to provide good circuit characteristics to reduce or minimize noise.